I'd hold off. It's stressful enough to split them. They've got a lot of brood they are trying to keep plenty warm. Disturbing this can't help them. Keep the queens fed and warm and wait for a little warmer weather.
No, 50's is not too cold to make splits...however, I wouldn't do it in the rain or wet weather. The brood will chill much quicker if they get wet when you are pulling the splits and then trying to intro the queens. 50's and sunny or cloudy and dry no problem.
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